The present invention relates to a braking device for an electric motor, in particular for an electric motor of a power tool. The present invention also relates to an electrical apparatus, such as for example a power tool, provided with a braking device. The invention also relates to a method of braking with the inventive braking device.
Hand power tools such as for example power drills and hand circular saws are driven by direct current series motors, which are identified as universal motors.
When such hand power tools are turned off, the direct current series motor, due to the mechanical inertia of the drive train, does not stop. This poses for the user the danger of an injury during running out.
For reducing this injury danger it is suggested in the European patent document EP0578366 A2 to provide a braking device for a direct current series motor, in which the armature winding of the direct current series motor can be short circuited by a short circuit switch to provide a braking action, so that the direct current series motor stops faster after the turning off. This braking action is produced in that the short circuit current in the armature winding forms a magnetic field which counteracts the outer magnetic field of the field winding of the direct current series motor.
The control of the short circuit switch is performed by the user of the hand power tool, wherein the main switch of the hand power tool is coupled with the short circuit switch. During turning off of the hand power tool by the user, simultaneously a closing of the short circuit switch is performed.